[postgres] retrieve foreign keys in determinist order (trial no. 2)

this failed on my macos as it returned keys in a different order,
e.g. nextras orm's users_x_users was returning pk foreign keys backwards

src/Platforms/PostgreSqlPlatform.php

@@ -163,7 +163,7 @@ public function getForeignKeys(string $table, ?string $schema = null): array
 				? "AND cl.oid = '%table.%table'::regclass"
 				: "AND cl.oid = '%table'::regclass"
 			) . '
-			ORDER BY atf.attnum
+			ORDER BY at.attnum
 			', ...$tableArgs);
 
 		$keys = [];